JP3024354B2 - Semiconductor laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser for optical communication, and more particularly to a semiconductor laser for an optical subscriber who is required to have excellent environmental resistance.

[0002]

2. Description of the Related Art A 1.3 μm band semiconductor laser for optical subscribers is required to have excellent environmental resistance performance.
An optical output of 8 mW or more when driven at 85 ° C. and 30 mA is required. However, in the case of a conventional laser having a bulk active layer, an oscillation operation at 85 ° C. and 30 mA could not be expected with a coating having a 70% reflectance on the back surface. On the other hand, Kamei et al.
Fiber Communication Conference (O
FC'91), a prototype of WM11 with a 90% coating on the back surface of a laser having a multiple quantum well active layer was reported at WM11 at 85 ° C and 30 mA.
The optical output at the time of driving is about 3 mW, which is not yet sufficient for optical subscribers. Each of these had a resonator length of 300 μm.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to greatly improve the temperature characteristics of such a conventional 1.3 .mu.m band semiconductor laser so that a driving current of about 30 mA even at a high temperature of 85.degree. An object of the present invention is to realize a long wavelength band or short wavelength band semiconductor laser which can obtain an output and can be sufficiently used for optical subscribers.

[0004]

SUMMARY OF THE INVENTION The present invention provides a DH on a substrate.
A semiconductor laser having a structure, wherein:
Light is emitted by a groove formed on one end face in the light emission direction.
A tip end face is formed, and the cavity length of the semiconductor laser is 15
It is not more than 0 μm .

Further, according to the present invention, in the above structure, a coating having a reflectance of 70% or more is applied to the light emitting end face opposite to the groove.

Further, according to the present invention, in the above structure, an optical fiber or an optical waveguide is coupled to the groove.
It is characterized by the following .

Further, according to the present invention, the multiple quantum well active layer is formed of In.
1.35 to 1.45 μm band gap that lattice matches with P
InGaAsP wells with a composition of 1.05 to 1.2 μm
Multi-layer with InGaAsP barrier of bandgap composition
In a quantum well semiconductor laser, the cavity length is 150 μm.
m and a coating having a reflectance of 90% or more on one end face. The long wavelength band is a 1 μm band, and particularly refers to a 1.3 to 1.5 μm band.

According to the present invention, the multiple quantum well active layer has a lattice matching of 1.35 to 1.45 μm with InP.
InGaAsP well with bandgap composition and 1.05
It is characterized by being composed of an InGaAsP barrier having a band gap composition of .about.1.2 .mu.m.

Further, according to the present invention, it is preferable that the number of wells of the multiple quantum well active layer be seven.

[0010]

The principle of the present invention will be described below. First,
In the semiconductor laser, the reason why the temperature characteristic is improved by shortening the cavity length to 150 μm or less and coating one end face with 90% or more will be briefly described.

In order to extract light output most efficiently from a semiconductor laser, it is necessary to set a threshold value at an optimum operating point that gives an appropriate resonator loss of a size commensurate with the internal gain. If the resonator loss is too small or too large compared to the internal gain, light output cannot be obtained efficiently. Since the cavity loss is determined by the internal loss, the cavity length, and the facet reflectivity, if the internal loss is known, the cavity length and the facet reflectivity can be appropriately selected according to the gain of the semiconductor laser. If so, optimal operating conditions should be obtained. For that purpose, first, values such as internal loss, internal quantum efficiency, gain constant, and current density at which gain starts to occur, which are basic device parameters of the semiconductor laser, must be obtained. The current-light output (IL) characteristics of the semiconductor laser can be calculated if these device parameters are known. Therefore, a multiple quantum well laser will be described as an example.
First, we prototyped various MQW lasers in the 1.3 μm band, measured the dependence of the threshold current and differential quantum efficiency on the cavity length, and started by obtaining the values of these device parameters.

Table 1 shows the device parameters obtained at 25 ° C. and 85 ° C. for one of the prototype 1.3 μm band MQW lasers. To perform an optimal design at a high temperature, it is necessary to know the value at that temperature.

[0013]

[Table 1]

FIG. 3 shows an IL at 85 ° C. of a 1.3 μm band MQW laser calculated using these parameters.
Show characteristics. As shown in the figure, it can be seen that the characteristics can be significantly improved by making the resonator as short as 150 μm and applying a coating having a high reflectance of 99% on the back surface. Originally MQ
Since a W laser has a larger gain than a bulk laser, a sufficient gain can be obtained even with a short resonator, so that the threshold value is lowered and the drive current can be reduced. still,
Lasers with well compositions of 1.35 μm composition and 1.40 μm composition were fabricated, these device parameters were evaluated, and the IL characteristics were calculated. It was found that 1.40 μm was 85% better than 1.35 μm. It was found that the characteristics at ° C were improved. Also, the number of wells is 7 layers, 10 layers, 18 layers.
Layers and 22 layers were prototyped and evaluated. The drive current of the 7 layers was the smallest.

Based on these experimental results, it can be seen that temperature characteristics can be significantly improved by combining an MQW laser with a short cavity length of 150 μm or less and an end face coating of 90% or more. The temperature characteristics of the laser of the bulk active layer are also improved for the same reason.

[0016]

Next, an embodiment of the present invention will be described with reference to the drawings.

FIGS. 1A and 1B are an external view and a diagram showing a mounting method of an InGaAsP / InP semiconductor laser 11 according to a first embodiment of the present invention, respectively. In manufacturing this device, first, a DH wafer for laser is manufactured by MOVPE growth, and CD-P is grown by LPE growth.
Embed in BH structure. Next, a p-side electrode is deposited, and a resist mask is formed thereon. After the electrode is further removed by etching, a groove 12 as shown in the figure is formed on one end surface side of the laser by wet etching. In this case, by forming the groove, the formation of one light emitting end face of the laser is also performed at the same time. 13 is an active layer. And the substrate is about 150
After polishing to a thickness of μm, an electrode is also formed on the n-side. Finally, the cavity is cleaved so as to have a cavity length of about 150 μm, and the cleaved surface is composed of a total of seven layers of λ / 4 SiO ₂ / Si.
After forming the high-reflection coating 14 having a reflectance of not less than%, the chip was cut into chips.

The device fabricated according to the above-described steps was mounted on a heat sink 15 made of silicon as shown in FIG. 1B, and bonded to an optical fiber 16 along the groove, and the characteristics were evaluated. Approximately 80% of the cut out devices oscillated, confirming that a good yield was obtained. At a driving current of 85 ° C. and 40 mA, an optical output in the fiber of 3 mW was obtained, indicating that this element has good temperature characteristics.

FIGS. 2A and 2B are an external view and a diagram showing a mounting method of an InGaAsP / InP semiconductor laser 21 according to a second embodiment of the present invention, respectively. In manufacturing this element, as in the first embodiment, first, a laser wafer is manufactured, a p-side electrode is deposited, and a resist mask is formed thereon. Further, after the electrode is removed by etching, a groove 22 as shown in the figure is formed on one end surface side of the laser by dry etching. In this case, by forming the groove, the formation of one light emitting end face of the laser is also performed at the same time. 23 is an active layer. And the substrate is about 150μ
After polishing to a thickness of m, an electrode is also formed on the n-side. Finally, the cavity is cleaved so as to have a cavity length of about 150 μm. After forming a high-reflection coating 24 having a reflectance of 70% or more consisting of 7 layers of λ / 4Si ₂ / Si on the cleaved surface, the chip is cut out. Was.

The device fabricated according to the above-described steps was coupled along the groove with the quartz optical waveguide 26 formed on the silicon substrate 25 as shown in FIG. 2B, and the characteristics were evaluated. . Approximately 70% of the cut out devices oscillated, confirming that a good yield was obtained.
At a driving current of 85 ° C. and 40 mA, an optical output in the waveguide of 2 mW was obtained, which indicates that this element has good temperature characteristics.

The semiconductor laser of the present invention is useful not only as a laser having a hostile specification requiring excellent environmental resistance performance, but also as a semiconductor laser for a small optical subscriber package because of easy optical mounting. . A similar structure is made of AlGaAs / GaAs or AlGaIn.
It can also be applied to P / GaAs-based short wavelength lasers.

A third embodiment of the present invention will be described with reference to FIG.

In manufacturing this device, first, a decompression MO
An MQW wafer is manufactured by VPE growth. FIG.
The band diagram of the W active layer is shown.
Angstrom thickness 1.40 μm composition InGaAsP
32, the barrier is 100Å thick 1.13μ
The 7-layer MQW is made of 1.13 μm InG having a thickness of 600 angstroms on both sides of the m-layer InGaAsP33.
It is sandwiched between aAsP guide layers. The wafer was subsequently embedded in a DC-PBH structure by LPE growth, a mesa electrode was formed on the p-side, the wafer was polished to a thickness of about 150 μm, and an electrode was deposited on the n-side. Finally, the cavity is cleaved so that the cavity length becomes about 150 μm, and λ / 4
After forming a high reflection film composed of a total of seven layers of SiO ₂ / Si,
Cut into chips.

The device manufactured according to the above steps was evaluated. FIG. 5 shows the IL characteristics of the pulse of the prototype device. The light output of 8 mW or more was obtained at a driving current of 85 ° C. and 30 mA, indicating that the device has good temperature characteristics.

The semiconductor laser of the present invention can be applied not only to a 1.3 μm band semiconductor laser for optical subscribers but also to a 1.5 μm band laser which is required to have excellent environmental resistance. Further, InGaAs may be obtained for the active layer.

[0026]

According to the present invention, a semiconductor laser having excellent temperature characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a semiconductor laser according to a first embodiment of the present invention.

FIG. 2 is a diagram for explaining a semiconductor laser according to a second embodiment of the present invention.

FIG. 3 is a diagram showing calculation results of IL characteristics for explaining the principle of the present invention.

FIG. 4 is a band diagram of an active layer for explaining a semiconductor laser according to a third embodiment of the present invention.

FIG. 5 is a diagram of a pulse IL characteristic for explaining a third embodiment of the present invention.

[Explanation of symbols]

11, 21 semiconductor laser 12, 22 groove 13, 23 the active layer 14 and 24 highly reflective coating 15 the heat sink 16 optical fiber 25 silicon substrate 26 of quartz optical waveguide _{31 InP 32 InGaAsP (λ g =} 1.40μm) 33 InGaAsP (λ g = 1.13 μm)

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-226978 (JP, A) JP-A-52-146189 (JP, A) JP-A-63-181489 (JP, A) Furukawa Electric Time Report No. 85 No. p. 20-28 (1989/12/28) Applied Physics Letters Vol. 60, no. 15, pp. 1782-1784 (1992/4/13) IEICE Technical Report Vol. 91, No. 75, pp 67-72 (May 27, 1991) IEEE JOURNAL OF QUANTUM ELECTRONIC S, Vol. QE-21, No. 12, p.p. 1958-1963 (1985/12 /) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01S 5/00-5/50 JICST file (JOIS)

Claims (5)

(57) [Claims] 1. A semiconductor laser having a DH structure on a substrate.
A light emitting direction on one end face side of the semiconductor element.
The light emitting end face is formed by the groove formed in
The resonator length of the semiconductor laser is 150 μm or less.
Semiconductor laser. 2. A coating having a reflectance of 70% or more on an end face opposite to the groove.
The semiconductor laser according to claim 1 . 3. An optical fiber or optical waveguide in the groove portion.
3. The half according to claim 1, wherein
Conductive laser. 4. The multiple quantum well active layer is lattice-matched with InP.
Of 1.35 to 1.45 μm band gap composition
GaAsP well and 1.05 to 1.2 μm band gap
Quantum Well Half with InGaAsP Barrier of Step Composition
1. A semiconductor laser, wherein a cavity length is 150 μm or less and a coating having a reflectance of 90% or more is applied to one end face. 5. The method according to claim 1, wherein the number of wells comprises seven layers.
The semiconductor laser according to claim 4.